Thilo Pauly, CERN/PH, LECC Heidelberg 2005 Sept 13, 2005 ATLAS Level-1 Trigger Timing-In Strategies On behalf of S. Ask 1), P. Borrego Amaral 1), N. Ellis 1), P. Farthouat 1), P. Gallno 1), J. Haller 1), A. Krasznahorkay 1)2), T. Maeno 1), T. Pauly 1), H. Pessoa Lima Jr. 3)4), I. Resurreccion Arcas 1), G. Schuler 1), J. M. de Seixas 3), R. Spiwoks 1), R. Torga Teixeira 1), T. Wengler 1) 1) CERN, Switzerland 2) University of Debrecen, Hungary 3) Federal University of Rio de Janeiro, Brazil 4) Brazilian Center for Research in Physics, Brazil

Thilo Pauly, CERN/PH, LECC Heidelberg 20052Sept 13, 2005 Timing Concept in the Trigger System Synchronous Asynchronous Identifier-based (L1ID, BCID) Timing-based (Subject of this talk) Trigger Delay L1A Delay

Thilo Pauly, CERN/PH, LECC Heidelberg 20053Sept 13, 2005 USA 15 Time of flight (bunches every 25ns = 7.5m) Detector response Cable lengths (10m = 100ns) The Problem Need well-defined procedures to do the timing-in. BC 2 BC 1

Thilo Pauly, CERN/PH, LECC Heidelberg 20054Sept 13, 2005 Overview Timing Signals at ATLAS –Distribution –Local Trigger Processor –Timing Tasks ATLAS Timing-In Strategy: –Test Pulses  Decent initial timing –Beam Pick-Up Detectors  Filled-Bunch Trigger  Bunch-Crossing Trigger NEW: Read-out of the Beam Pick-Up Detectors –Beam Pick-up Signal –Global BC Identification with Filled-Bunch Trigger –Clock phase: Read-out system, test results Conclusions

Thilo Pauly, CERN/PH, LECC Heidelberg 20055Sept 13, 2005 Timing Signals from the CTP Level-1 Accept (L1A) BC = Bunch Clock with MHz Orbit Signal: –1 μs long pulse every revolution (89 μs) –Is used as bunch counter reset (BCR) to synchronise the BC counters in the sub-detector front-ends, i.e. BCID –An LHC cycle consists of bunches, each uniquely identified by a BCID number. –As reference point the abort gap in the bunch train can be used.

Thilo Pauly, CERN/PH, LECC Heidelberg 20056Sept 13, 2005 Distribution of Timing Signals CTP distributes L1A, BC, Orbit through CTP_OUT (see R. Spiwoks “The ATLAS Level-1 Central Trigger Processor”) Local Trigger Processor (LTP): –Interface to CTP when running in global mode –Important tool for sub-system timing-in –Replaces the CTP when running in local mode (test-pulses) Via the TTC system (Timing, Trigger and Controls) New Multiplexer Module for combining partitions CTP Up to 20 Links Partitions

Thilo Pauly, CERN/PH, LECC Heidelberg 20057Sept 13, 2005 Local Trigger Processor CTP Local Calibration Request Trigger Type LTP2 Interface to CTP + CTP Replacement for Local Mode (Local Inputs, Pattern Generator) + Programmable Switch Manual: ATL-DA-ES-0033 max 30 m TTC

Thilo Pauly, CERN/PH, LECC Heidelberg 20058Sept 13, 2005 Typical Timing Tasks Sub-detector-specific Timing Tasks Global Timing Adjustments BC Counter for BCID Processing TTC Distribution Data Forming (Phase between BC & Signal) Data Alignment (in steps of 25ns) BC Identification (BCR delay) Triggered BC Identification (L1A delay) BC BCR L1A Sub-detector

Thilo Pauly, CERN/PH, LECC Heidelberg 20059Sept 13, 2005 Scenarios for Timing-In Timing-in with test-pulses: –Local mode: Stand-alone sub-detector timing-in, without the CTP, only with LTP –Global mode with CTP Will already give a decent initial timing set-up (up to a few bunch crossings) Single Beams: –Beam pick-ups to see filled bunches –CTP can be programmed to trigger on specific filled bunches: filled-bunch trigger, bunch-crossing trigger Collisions: –Scintillation-counter hodoscopes in front of the end-cap calorimeter –Coincidence between the two ends will give minimum bias trigger (also combination with bunch-crossing trigger)

Thilo Pauly, CERN/PH, LECC Heidelberg Sept 13, 2005 Timing-In with Test-Pulses in Local Mode LTP issues a L1A a fixed time Δt after a pre-pulse, synchronised with the ORBIT LTP should simulate CTP (same phase with Orbit as for global mode) Predict beam-beam timing (d gen ) with simulation of: –Time-of-flight –Detector response –Calibration system specific delays Also account for expected trigger latency and propagation of L1A signal Adjust L1A delay (d L1A ): scan and recover test-pulse data Test-Signal Generator d gen d L1A LTP Pre-pulse L1A ΔtΔt Sub-detector

Thilo Pauly, CERN/PH, LECC Heidelberg Sept 13, 2005 Timing-In with Test-Pulses in Global Mode Central Trigger Processor (CTP) triggers on a fixed BCID. LTP now in transparent mode BC identification by comparing BCIDs of event fragments in the read-out events (BCR offsets) Good initial timing setup for beam-beam collisions (up to a few bunch crossings) Leaves only the global timing to be established later: –Single beams: global BCR delay –Collisions: clock phase, global L1A Test-Signal Generator LTPLTP Test-Signal Generator LTPLTP CTPCTP

Thilo Pauly, CERN/PH, LECC Heidelberg Sept 13, 2005 Timing-In With Beam Need to “see” the bunches BPTX = Beam position monitors for timing purposes Timing reference wrt bunches 1 per incoming beam, 175 m from IP Electro-static button electrodes Read-out currently under study

Thilo Pauly, CERN/PH, LECC Heidelberg Sept 13, 2005 Usage of the BPTX Signal BPTX are very powerful: 1.Filled-bunch trigger, Bunch-crossing trigger 2.Very precise time reference (clock monitoring) “TTC Machine Interface” BC-Ref BC-RF1 BC-RF2 BPTX Read-out System (Oscilloscopes + Computer) BC-Ref Orbit BC-RF1 BC-RF2 BPTX1/2 Optical Electrical Apps Database Configuration/ Steering Discr. CTP USA15 Electrical Orbit 200m (few ns) (20 ps) Filled-Bunch Trigger Monitoring

Thilo Pauly, CERN/PH, LECC Heidelberg Sept 13, 2005 Usage of the BPTX Signal 1)Filled-bunch trigger: Global BC Identification  Trigger input for CTP for filled-bunch trigger (Discrimination of the bunch signals by preserving the time information of each bunch at the level of a few ns)  Detection of gaps in the bunch train with CTP bunch-to-bunch scalers of trigger inputs (CTPMON) BCID BC=0

Thilo Pauly, CERN/PH, LECC Heidelberg Sept 13, 2005 Usage of the BPTX Signal 2)Clock Monitoring: Check the phase of each individual bunch with the phase of the clock (accuracy: ~20ps ) Monitoring of the clock from the machine. Detection of clock drift, due to  Problems in the signal chain  Temperature drifts in optical fibres Check for satellite bunches in RF buckets (2.5ns) Monitoring frequency ~ once per minute

Thilo Pauly, CERN/PH, LECC Heidelberg Sept 13, 2005 Expected BPTX Signal Very clean signal +20V V on 50Ω per button (from calculation, no transmission line yet) After transmission line: 20% of amplitude Simple discrimination: –Zero-crossing independent of bunch intensity –Zero-crossing depends on bunch length: –Bunch length fluctuations at 7 TeV will be %-level Nominal LHC intensity: 1.15 x p/bunch 7 TeV

Thilo Pauly, CERN/PH, LECC Heidelberg Sept 13, 2005 Information in the BPTX Signal –Complete signal description exists, and can be used as a fit function. Fit parameters: t 0 Time of closest approach of bunch to BPTX, NNumber of protons in bunch σBunch length (Gaussian σ) –Background is expected to be small and under control (noise, reflections, etc.)

Thilo Pauly, CERN/PH, LECC Heidelberg Sept 13, 2005 Clock Phase wrt LHC Bunches Resolution to be 20 ps NEW: Read-out with oscilloscopes –Relatively cheap (several 10 kCHF), no hardware and low-level software development –Guaranteed support –Signal is fully visible, no signal discrimination before read-out: necessary for debugging –Usually maximum of 4 Channels: 2 scopes required for 6 signals. For instance: Scope 1: Orbit, BC-Ref, BC-RF1, BPTX1 Scope 2: Orbit, BC-Ref, BC-RF2, BPTX2

Thilo Pauly, CERN/PH, LECC Heidelberg Sept 13, 2005 Test system with Tektronix TDS 3054B –5 GS/s real-time sampling rate, i.e. measurements every 200ps –Memory depth: 10k, i.e. 2μs (Read out 45 chunks of 2μs) –Max voltage on 50Ω: 5V RMS with peaks < ±30V –8-bit vertical resolution, ~0.3% –4 channels –Trigger on long-gap with hold-off time to μs-x (with x < 2.75μs) –BPTX Test signal: Shaped output from a pattern generator (Local Trigger Processor) –Built-in ethernet port: configuration and read-out through HTTP1.1 –Data analysis with ROOT and MINUIT

Thilo Pauly, CERN/PH, LECC Heidelberg Sept 13, 2005 Test Result: Proof of Principle with TDS 3054B Clock BPTX Test Signal Clock fit Signal fit Read out via HTTP1.1

Thilo Pauly, CERN/PH, LECC Heidelberg Sept 13, 2005 BPTX resolutions: Toy-Simulation, 1000 samples, TDS3054B resolutions (vertical resolution: 0.2V) t 0 = 0 ± 2.6ps σ = 252ps ± 3.0ps N = (1.150 ± 0.015) x t 0 uncorrelated to σ, N Correlation between σ and N: 0.68 Test Result: Resolutions Clock Phase resolution: –Difference of two consecutive clock signals –Resolution of phase measurement: 20ps –Resolution of single time measurement: 20ps/√2 = 14ps Measured Simulated

Thilo Pauly, CERN/PH, LECC Heidelberg Sept 13, 2005 BPTX Read-Out: Conclusions The read-out requirements for the ATLAS BPTX can be fulfilled with 2 modern off-the-shelf sampling oscilloscopes with: –4 channels each –Sampling rate ≥ 5 GS/sec –Memory deep enough to accommodate 89μs –Communication via ethernet

Thilo Pauly, CERN/PH, LECC Heidelberg Sept 13, 2005 Conclusion I have presented strategies for timing in the sub-detectors –With test-pulses in local and global mode a good initial timing setup can be achieved: up to a few bunch crossings ATLAS beam pick-up detectors are very powerful for timing-in with beam: –Filled-bunch trigger: Global BC identification –Measuring and monitoring of the clock phase wrt LHC bunches

Thilo Pauly, CERN/PH, LECC Heidelberg Sept 13, 2005 Backup slides

Thilo Pauly, CERN/PH, LECC Heidelberg Sept 13, 2005 Minimum-bias trigger: One hodoscope plane on each side replacing part of the JM moderator between Inner Detector and LAr Scintillator Counter Hodoscope η coverage: z = ± 3.5 m ~25 cm < R < ~115 cm  ~1.8 < η < ~3.3 φ segmentation: probably 8 Very high efficiency for minimum bias events

Thilo Pauly, CERN/PH, LECC Heidelberg Sept 13, 2005 The CTP is timed-in using the beam pick-ups as timing reference: CTP can generate triggers with a fixed latency for specific bunch crossings using the beam pickups Using the scintillatior hodoscopes, the CTP can restrict triggers to crossings with interactions Timing-In CTP Using the Beam Structure Adjust offset BCID LHC BCID CTP

Thilo Pauly, CERN/PH, LECC Heidelberg Sept 13, )Sub-detector chooses a quantity with high rate due to interaction products and small background from other sources 2)Map out the LHC bunch structure by plotting activity vs. BCID using random triggers or scanning all BCID values with L1As 3)Compare to (known) LHC bunch structure, e.g. position of long gap Timing Check Using the Beam Structure Adjust for offsets But: this procedure can take several days for certain sub- detectors with low rate and acceptance.

Thilo Pauly, CERN/PH, LECC Heidelberg Sept 13, 2005 Global BC Identification with Filled-Bunch Trigger Discriminate BPTX signal (at the ns level) Propagation of BPTX signal into CTP is known ToF from BPTX position to z=0 is known CTP has scalers for each PIT bit and each single bunch: find abort gap for the BPTX trigger signal BC=0 BCID

Thilo Pauly, CERN/PH, LECC Heidelberg Sept 13, 2005 BPTX Signal Expectation Longitudinally Gaussian-shaped bunch produces a current of mirror charge on the button surface, which gives a voltage signal on the transfer impedance: Basic model: “Differentiated Gaussian convolved with an exponential due to the RC” Transfer Impedance Z T = 1.04Ω Read-out 50Ω BPTX Bunch N protons length σ 16pF u R (t) (no transmission line yet)

Thilo Pauly, CERN/PH, LECC Heidelberg Sept 13, 2005 Expected BPTX Signal Very clean signal +20V V on 50Ω per button (from calculation, no transmission line yet) Zero-crossing independent of bunch intensity Zero-crossing depends on bunch length: –100ps effect between injection and 7 TeV –Bunch length fluctuations at 7 TeV will be %-level Nominal LHC intensity: 1.15 x p/bunch At Injection At 7 TeV 7 TeV5 x 10 9 p/bunch

Thilo Pauly, CERN/PH, LECC Heidelberg Sept 13, 2005 Acquisition Mode/Scope Trigger Acquisition modes: –Real-time sampling (single shot, averaging mode) –Equivalent-time sampling (only for repetitive signals) Different trigger possibilities: –For a real-time single shot mode, any trigger can be used: whole bunch train is read out. –For averaging or equivalent-time sampling, a trigger signal with small jitter is needed. Possibilities: Orbit signal Combination: First Orbit, then clock edge BPTX signal itself, with trigger hold-off time set to find particular gaps in the bunch train